1. Field of the Invention
The present invention relates to a device for connecting vertebrae of the vertebral or spinal column through an implant to be arranged between the vertebrae. The implant has at least one hollow space and openings to allow bone tissue formed for connecting the vertebrae to grow into the implant.
2. Description of the Related Art
When vertebrae are connected, for example, after an intervertebral disk resection, such an implant stabilizes the vertebral column as long as not sufficient connecting bone tissue has formed.
Implants having a cylindrical configuration are known in the art. These implants are provided with an external thread which can be screwed into a prepared threaded bore which has threaded portions in the vertebrae to be connected and located opposite at a distance from each other. When the threaded portions are prepared, the hard bone tissue layer is removed to such an extent that the cylindrical implants come over a portion of their circumference in contact with the underlying soft bone tissue. It is only the soft bone tissue which is capable of forming connecting bone tissue which can grow through openings in the cylinder wall of the implant and can extend through the implant.
Also known in the art are implants which have a parallelepiped-shaped configuration. When these implants are implanted, appropriate cuts have to be prepared in the oppositely located end faces of the vertebrae in order to make it possible that the exposed soft bone tissue forms connecting tissue which can grow through the implant.
It is the primary object of the present invention to provide a novel device for connecting vertebrae of the vertebral column of the above-described type which, compared to conventional devices, better stabilizes the vertebral column during the growth of the connecting bone tissue and ensures a more exact positioning of the vertebrae within the vertebral column.
In accordance with the present invention, the implant includes a connecting portion to be placed against exposed soft bone tissue and at least one spacer portion protruding from the connecting portion to be placed against hard bone tissue.
The implant according to the present invention makes it possible that a vertical load can be placed on the vertebral column, wherein the spacer portions resting against the hard bone tissue ensure that the vertebrae maintain their required positions within the vertebral column. In implants according to the prior art, it can easily happen that the implant is pressed into the soft bone tissue and the distance between the vertebrae is undesirably reduced.
In accordance with a preferred embodiment of the invention, the connecting part has an essentially rotationally symmetrical configuration, for example, in the form of a cylinder or a conical section. In that case, the work to be carried out on the bone for exposing the soft bone tissue can be carried out with a drilling or milling cutting tool, wherein the dimensions of the drilled or cut areas formed as a result are essentially determined by the dimensions of the tool. In order to work on the bone, the tool merely has to be advanced by a required distance and no further movement of the tool is required for carrying out the work.
In accordance with a preferred feature, the spacer portions are constructed as spacer wings which extend especially diametrically oppositely from the connecting portion. While the connecting portion is in contact with soft bone tissue and extends into a drilled or cut area, the two spacer wings extending on both sides of the connecting portion rest against the hard bone tissue of the upper and lower vertebrae which is located adjacent the respective drilled or cut area.
In accordance with another embodiment of the invention, the connecting portion and at least one spacer portion taper corresponding to the vertebrae which are arranged inclined relative to each other. This embodiment is provided for connecting those vertebrae which are part of the curved portions of the vertebral column.
The hollow space mentioned above may extend into the spacer portion so that connecting bone tissue can also grow into the spacer portion.
In accordance with a preferred feature, the implant is formed as a hollow body with walls for forming openings in the manner of a cage. In particular, the connecting portion has opening slots which extend transversely of the rotational axis direction of the implant. The connecting bone tissue which is formed penetrates through these opening slots into the hollow body and engages behind the walls of the hollow body.
The opening slots may extend beyond the connecting portion into the spacer portions. In addition, the spacer wings may at their wing ends be provided with cutouts, so that connecting bone tissue can also grow into the spacer portions.
In accordance with another preferred embodiment of the invention, the hollow body has on one end face an end wall particularly provided with cutouts, wherein the hollow body is open at the other end face. Such a hollow body can be inserted with the closed end wall side facing forward into the intermediate space between the vertebrae to be connected, wherein, for example, support tools can be inserted into the hollow body of the implant through the other open end face. The end wall also serves to secure filling material which can be filled in order to facilitate the growth of bone tissue into the hollow body.
In accordance with a further development of the invention, a locking device is provided for securing the implant transversely of the longitudinal direction of the vertebral column, wherein the locking device ensures that the implant cannot move out of the intermediate space between the vertebrae to be connected. Such a locking device may include an insert which can be introduced into the implant and which has a hook-type device which engages especially into the soft bone tissue.
In accordance with a preferred embodiment, the hook-type device has hook portions which are arranged on an insert body which is rotatable in the implant in the manner of a cylinder lock, wherein the hook-portions can be turned through the opening slots into the soft bone tissue. Such an insert with hook portions can be inserted into the implant, wherein the hook portions move within the spacer wings. The opening slots extending up to the spacer wings ensure that when the insert body is turned the hook portions can protrude through the opening slots into the soft bone tissue and provide a hook-like connection of the implant in this manner.
The insert can be secured in the implant between the end wall mentioned above and a locking member which can be mounted on the other end face, wherein the locking member preferably used is a headless screw which can be retracted in the implant.
In accordance with an advantageous feature, the insert can be secured in the implant with a predetermined play which is so small that it does not impair the precise positioning of the vertebrae, wherein, however, slight movements of the locking insert hooked into the soft bone tissue promote the growth of connecting bone tissue.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.